With the water in the test kettle cold (about 60°F) and compressed air applied to the "from engine" connection air came through the "to cooler" connection only.

However with the finger restriction placed on the "to cooler" connection - largely but not completely blocking the open end of the tube - a large amount of bubbles came from both the "from cooler" and "to oil tank" connections.

The water heater was then switched on and the water brought to boiling point.

With the same degree of finger restriction there were no bubbles from the "to oil tank" and "from cooler" connections.

The water was then allowed to cool naturally and the test repeated at different lower temperatures as the water cooled down.

At 185°F with the finger restriction as before some bubbles came from the "from cooler" connection.

At both 170°F and 160°F the results were the same as at 185°F.

At 150°F the results were the same as at 60°F.

These results show that the TC unit operates at around the 185°F design point and on cooling down returns to the "cold" condition of between 150°F and 160°F.

This is basically what one would expect.